XRP7665IDBTR-F

XRP7665 3A 18V Synchronous Step-Down Converter March 2013 Rev. 2.0.1 GENERAL DESCRIPTION APPLICATIONS The XRP7665 is a synchronous current-mode PWM step down (buck) regulator capable of a constant output current up to 3 Amps. A wide 4.50V to 18V input voltage range allows for single supply operations from industry standard 5V and 12V power rails. With a 340kHz constant operating frequency and integrated high and low side 100mΩ/90mΩ MOSFETs, the XRP7665 reduces the overall component count and solution footprint. Current-mode control provides fast transient response and cycle-by-cycle current limit. An adjustable soft-start prevents inrush current at turn-on, and in shutdown mode the supply current drops to 0.1µA. Built-in output over voltage (open load), over temperature, cycle-by-cycle over current and under voltage lockout (UVLO) protections insure safe operations under abnormal operating conditions. The XRP7665 is a pin and function compatible device to MP1484 and a 3A pin to pin upgrade to XRP7664. The XRP7665 is offered in a RoHS compliant, “green”/halogen free 8-pin exposed pad SOIC package.  Distributed Power Architectures  Point of Load Converters  Audio-Video Equipments  Medical & Industrial Equipments FEATURES  Pin/Function Compatible to MP1484  3A Continuous Output Current  4.50V to 18V Wide Input Voltage  PWM Current Mode Control  340kHz Constant Operations  Up to 93% Efficiency  Adjustable Output Voltage  0.925V to 16V Range  2.0% Accuracy  Programmable Soft-Start and Enable Function  Built-in Thermal, Over Current, UVLO and Output Over Voltage Protections  RoHS Compliant “Green”/Halogen Free 8-Pin Exposed Pad SOIC Package TYPICAL APPLICATION DIAGRAM Fig. 1: XRP7665 Application Diagram Exar Corporation 48720 Kato Road, Fremont CA 94538, USA www.exar.com Tel. +1 510 668-7000 – Fax. +1 510 668-7001 XRP7665 3A 18V Synchronous Step-Down Converter ABSOLUTE MAXIMUM RATINGS OPERATING RATINGS These are stress ratings only and functional operation of the device at these ratings or any other above those indicated in the operation sections of the specifications below is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability. Input Voltage VIN ....................................... 4.50V to 18V Ambient Operating Temperature ................ -40°C to 85°C Maximum Output Current.................................... 3A min Thermal Resistance θJA ...................................... 60°C/W Supply Voltage VIN ...................................... -0.3V to 20V Switch Node Voltage VSW ......................................... 21V Boost Voltage VBS ................................... -0.3 to VSW+6V Enable Voltage VEN ......................................... -0.3 to VIN All Other Pins .............................................. -0.3 to +6V Junction Temperature .......................................... 150°C Storage Temperature .............................. -65°C to 150°C Lead Temperature (Soldering, 10 sec) ................... 260°C ESD Rating (HBM - Human Body Model) .................... 2kV ESD Rating (MM - Machine Model) ...........................200V Moisture Sensitivity Level (MSL) ................................... 3 ELECTRICAL SPECIFICATIONS Specifications are for an Operating Ambient Temperature of TA = 25°C only; limits applying over the full Ambient Operating Temperature range are denoted by a “•”. Minimum and Maximum limits are guaranteed through test, design, or statistical correlation. Typical values represent the most likely parametric norm at TA = 25°C, and are provided for reference purposes only. Unless otherwise indicated, VIN = VEN = 12V, VOUT=3.3V. Typ. Max. Units Shutdown Supply Current Parameter 0.1 10 µA VEN≤0.75V Quiescent Current 1.2 1.4 mA VEN=3V, VFB=1V 0.925 0.943 V 0.1 µA Feedback Voltage VFB Min. 0.907 Feedback Overvoltage Threshold Feedback Bias Current 1.1 -0.1 Conditions V VFB=1V Error Amplifier Voltage Gain AEA (Note 1) 400 V/V Error Amplifier Transconductance GEA 800 µA/V High-Side switch On Resistance RDSONH (Note 2) 100 mΩ ISW=0.2A&0.7A Low-Side switch On Resistance RDSONL (Note 2) 100 mΩ ISW=-0.2A&-0.7A High-Side switch Leakage Current 0.1 µA VIN=18V, VEN=0V, VSW=0V High-Side Switch Current Limit 10 5.6 A Low-Side Switch Current Limit 1.4 A COMP to Current Sense Transconductance GCS 5.2 A/V Oscillator Frequency FOSC1 4.3 280 340 Short Circuit Oscillator Frequency FOSC2 90 Maximum Duty Cycle DMAX 90 Minimum Duty Cycle DMIN EN Enable Threshold Voltage 2.2 EN Enable Threshold Voltage Hysteresis (Note 1) UVLO Threshold © 2013 Exar Corporation 2.5 400 4.00 kHz kHz % VFB=0.85V 0 % VFB=1V 2.7 V 210 3.65 From Drain to Source mV 4.25 2/12 V VIN Rising Rev. 2.0.1 XRP7665 3A 18V Synchronous Step-Down Converter Parameter Min. UVLO Hysteresis Typ. Max. 0.20 Soft-start Current Soft-start Time (Note 1) Thermal Shutdown (Note 1) Thermal Shutdown Hysteresis (Note 1) Units Conditions V 6 µA VSS=0V 15 ms CSS=0.1µF 160 °C 20 °C Note 1: Guaranteed by design. Note 2: RDSON=(VSW1-VSW2)/(ISW1-ISW2) BLOCK DIAGRAM Fig. 2: XRP7665 Block Diagram PIN ASSIGNMENT Fig. 3: XRP7665 Pin Assignment (SOIC-8 Exposed Pad) © 2013 Exar Corporation 3/12 Rev. 2.0.1 XRP7665 3A 18V Synchronous Step-Down Converter PIN DESCRIPTION Name Pin Number Description BS 1 Bootstrap pin. Connect a 0.01µF or greater bootstrap capacitor between the BS pin and the SW pin. The voltage across the bootstrap capacitor drives the internal high-side power MOSFET. IN 2 Power input pin. A capacitor should be connected between the IN pin and GND pin to keep the input voltage constant. SW 3 Power switch output pin. This pin is connected to the inductor and the bootstrap capacitor. GND 4 Ground signal pin. FB 5 Feedback pin. An external resistor divider connected to FB programs the output voltage. If the feedback pin exceeds 1.1V the over-voltage protection will trigger. If the feedback voltage drops below 0.3V the oscillator frequency is lowered to achieve short-circuit protection. COMP 6 Compensation pin. This is the output of transconductance error amplifier and the input to the current comparator. It is used to compensate the control loop. Connect an RC network form this pin to GND. EN 7 Control input pin. Forcing this pin above 2.7V enables the IC. Forcing this pin below 0.75V shuts down the IC. Pull up to VIN with 100kΩ for automatic startup. SS 8 Soft-start control input pin. Connect a capacitor from SS to GND to set the soft-start period. A 0.1µF capacitor sets the soft start period to 15ms. To disable the soft-start feature, leave SS unconnected. - EP Exposed Pad Connect to GND through PCB. ORDERING INFORMATION Part Number XRP7665IDBTR-F XRP7665EVB Temperature Range Marking XRP7665I YYWWF X XRP7665 Evaluation Board -40°C≤TA≤+85°C Package Packing Quantity Note 1 Note 2 RoHS Compliant SOIC-8(EP) 2.5K/Tape & Reel Halogen Free “YY” = Year – “WW” = Work Week – “X” = Lot Number; when applicable. © 2013 Exar Corporation 4/12 Rev. 2.0.1 XRP7665 3A 18V Synchronous Step-Down Converter TYPICAL PERFORMANCE CHARACTERISTICS All data taken at VIN = 12V, VOUT=3.3V, TJ = TA = 25°C, unless otherwise specified - Schematic and BOM from Application Information section of this datasheet. Fig. 4: Efficiency versus output current Fig. 5: RDSONH versus case temperature Fig. 6: RDSONL versus case temperature Fig. 7: Feedback voltage versus case temperature Fig. 8: Quiescent current versus case temperature Fig. 9: Output voltage versus output current © 2013 Exar Corporation 5/12 Rev. 2.0.1 XRP7665 3A 18V Synchronous Step-Down Converter Fig. 10: Output voltage ripple, IOUT=3A Fig. 11: Load transient (IOUT=1.5A to 3A) Fig. 12: Enable turn on CC mode, VIN=12V, VOUT=VEN=3.3, IOUT=3A Fig. 13: Enable turn off CC mode, VIN=12V, VOUT=VEN=3.3, IOUT=3A Fig. 14: Short-circuit protection Fig. 15: Short-circuit recovery © 2013 Exar Corporation 6/12 Rev. 2.0.1 XRP7665 3A 18V Synchronous Step-Down Converter THEORY OF OPERATION OVERCURRENT PROTECTION OCP The OCP protects against accidental increase in load current that can cause the regulator to fail. The current of internal switch M1 is monitored. If this current reaches 5.6A then M1 is turned off until next switching cycle. FUNCTIONAL DESCRIPTION The XRP7665 is a synchronous, current-mode, step-down regulator. It regulates input voltages from 4.5V to 18V and supplies up to 3A of continuous load current. The XRP7665 uses current-mode control to regulate the output voltage. The output voltage is measured at FB through a resistive voltage divider and input to a transconductance error amplifier. The high-side switch current is compared to the output of the error amplifier to control the output voltage. The regulator utilizes internal N-channel MOSFETs to stepdown the input voltage. A bootstrapping capacitor connected between BS and SW acts as a supply for high-side MOSFET. This capacitor is charged from the internal 5V supply when SW node is low. The XRP7665 has several powerful protection features including OCP, OVP, OTP, UVLO and output short-circuit. SHORT-CIRCUIT PROTECTION If there is short-circuit across the output, the feedback voltage VFB will droop. If VFB drops below 0.3V the XRP7665 will detect a shortcircuit condition and reduce the switching frequency to 90kHz for system protection. The regulator will restart once the short-circuit has been removed. OVERVOLTAGE PROTECTION OVP The XRP7665 has internal OVP. When VOUT exceeds the OVP threshold (when VFB exceeds 1.1V) the power switching will be turned off. The XRP7665 will restart when overvoltage condition is removed. PROGRAMMABLE SOFT-START OVER-TEMPERATURE PROTECTION OTP The soft-start time is fully programmable via CSS capacitor, placed between the SS and GND pin. The CSS is charged by a 6µA constant-current source, generating a ramp signal fed into non-inverting input of the error amplifier. This ramp regulates the voltage on comp pin during the regulator startup, thus realizing soft-start. Calculate the required CSS from: If the junction temperature exceeds 160°C the OTP circuit is triggered, turning off the internal control circuit and switched M1 and M2. When junction temperature drops below 140°C the XRP7665 will restart. APPLICATION INFORMATION SETTING THE OUTPUT VOLTAGE Where: Use an external resistor divider to set the output voltage. Program the output voltage from: tss is the required soft-start time VFB is the feedback voltage (0.925V nominal) ENABLE FUNCTION Where: The XRP7665 is enabled by raising the voltage on the EN pin above 2.5V nominally. Connect the EN pin to the VIN via a 100kΩ resistor for automatic start-up. Shutdown is achieved by pulling the EN pin voltage below 1.1V nominally. © 2013 Exar Corporation R1 is the resistor between VOUT and FB R2 is the resistor between FB and GND (nominally 10kΩ) 0.925V is the nominal feedback voltage. 7/12 Rev. 2.0.1 XRP7665 3A 18V Synchronous Step-Down Converter of thumb, should be at least twice the output voltage. When calculating the required capacitance, usually the overriding requirement is current load-step transient. If the unloading transient (i.e., when load transitions from a high to a low current) is met, then usually the loading transient (when load transitions from a low to a high current) is met as well. Therefore calculate the COUT based on the unloading transient requirement from: OUTPUT INDUCTOR Select the output inductor for inductance L, DC current rating IDC and saturation current rating ISAT. IDC should be larger than regulator output current. ISAT, as a rule of thumb, should be 50% higher than the regulator output current. Since the regulator is rated at 3A then IDC≥3A and ISAT≥4.5A. Calculate the inductance from: Where: ΔIL is peak-to-peak inductor current ripple nominally set to 30%-40% of IOUT Where: fS is nominal switching frequency (340kHz) L is the inductance calculated in the preceding step As an example, inductor values for several common output voltages are shown in tables 1 and 2. Note that example inductors shown in tables 1 and 2 are Wurth shielded inductors. If the target application is not sensitive to EMI then unshielded inductors may be used. VOUT(V) ΔIL(p-p)(A) 5.0 3.3 2.5 1.8 1.5 1.2 L(µH) Inductor Example 10 10 10 7.6 7.6 4.9 744314101 744314101 744314101 744314760 744314760 744314490 0.9 0.7 0.6 0.6 0.5 0.6 IHigh is the value of load-step prior to unloading. This is nominally set equal to regulator current rating (3A). ILow is the value of load-step after unloading. This is nominally set equal to 50% of regulator current rating (1.5A). Vtransient is the maximum permissible voltage transient corresponding to the load step mentioned above. Vtransient is typically specified from 3% to 5% of VOUT. ESR of the capacitor has to be selected such that the output voltage ripple requirement ΔVOUT, nominally 1% of VOUT, is met. Voltage ripple ΔVOUT is mainly composed of two components: the resistive ripple due to ESR and capacitive ripple due to COUT charge transfer. For applications requiring low voltage ripple, ceramic capacitors are recommended because of their low ESR which is typically in the range of 5mΩ. Therefore ΔVOUT is mainly capacitive. For ceramic capacitors calculate the ΔVOUT from: Table 1: Suggested inductor values for VIN=12V and IOUT=3A VOUT(V) ΔIL(p-p)(A) 3.3 2.5 1.8 1.5 1.2 L(µH) Inductor Example 4.9 4.9 4.9 4.9 4.9 744314490 744314490 744314490 744314490 744314490 0.7 0.8 0.7 0.6 0.5 Table 2: Suggested inductor values for VIN=5V and IOUT=3A Where: ΔIL is from table 1 or 2 OUTPUT CAPACITOR COUT COUT is the value calculated above Select the output capacitor for voltage rating, capacitance COUT and Equivalent Series Resistance ESR. The voltage rating, as a rule fs is nominal switching frequency (340kHz) © 2013 Exar Corporation 8/12 Rev. 2.0.1 XRP7665 3A 18V Synchronous Step-Down Converter If tantalum or electrolytic capacitors are used then ΔVOUT is essentially a function of ESR: Circuit configuration is shown in figures 16 and 17. The external bootstrap diode is also recommended where duty cycle (VOUT/VIN) is larger than 65%. INPUT CAPACITOR CIN Select the input capacitor for voltage rating, RMS current rating and capacitance. The voltage rating should be at least 50% higher than the regulator’s maximum input voltage. Calculate the capacitor’s current rating from: 1N4148 VIN = 5V IN BS 10nF XRP7665 Where: SW IOUT is regulator’s maximum current (3A) Fig. 16: Optional external bootstrap diode where input voltage is fixed at 5V D is duty cycle (D=VOUT/VIN) Calculate the CIN capacitance from: 1N4148 BS Where: 10nF XRP7665 ΔVIN is the permissible input voltage ripple, nominally set at 1% of VIN VOUT = 5V or 3.3V SW COUT OPTIONAL SCHOTTKY DIODE An optional Schottky diode may be paralleled between the GND pin and SW pin to improve the regulator efficiency. Examples are shown in Table 3. Part Number Voltage/Current Rating B130 SK13 30V/1A 30V/1A MBRS130 30V/1A Fig. 17: Optional external bootstrap diode where output voltage is 5V or 3.3V LOOP COMPENSATION XRP7665 utilizes current-mode control. This allows using a minimum of external components to compensate the regulator. In general only two components are needed: RC and CC. Proper compensation of the regulator (determining RC and CC) results in optimum transient response. In terms of power supply control theory, the goals of compensation are to choose RC and CC such that the regulator loop gain has a crossover frequency fc between 15kHz and 34kHz. The corresponding phase-margin should be between 45 degrees and 65 degrees. An important characteristic of current-mode buck regulator is its dominant pole. The frequency of the dominant pole is given by: Vendor Diodes, Inc. Diodes, Inc. International Rectifier Table 3. Optional Schottky diode EXTERNAL BOOTSTRAP DIODE A low-cost diode, such as 1N4148, is recommended for higher efficiency when the input voltage is 5V or the output is 5V or 3.3V. © 2013 Exar Corporation 9/12 Rev. 2.0.1 XRP7665 3A 18V Synchronous Step-Down Converter XRP7665’s Error Amplifier and ground, constitute a zero. The frequency of this compensating zero is given by: where Rload is the output load resistance. The uncompensated regulator has a constant gain up to its pole frequency, beyond which the gain decreases at -20dB/decade. The zero arising from the output capacitor’s ESR is inconsequential if ceramic COUT is used. This simplifies the compensation. The RC and CC, which are placed between the output of For the typical application circuit, RC=6.8kΩ and CC=3.9nF provide a satisfactory compensation. Please contact EXAR if you need assistance with the compensation of your particular circuit. TYPICAL APPLICATIONS Fig. 18: XRP7665 Typical Application Diagram - 12V to 3.3V Conversion © 2013 Exar Corporation 10/12 Rev. 2.0.1 XRP7665 3A 18V Synchronous Step-Down Converter PACKAGE SPECIFICATION 8-PIN SOIC EXPOSED PAD Unit: mm (inch) Eject hole, oriented hole and mold mark are optional. © 2013 Exar Corporation 11/12 Rev. 2.0.1 XRP7665 3A 18V Synchronous Step-Down Converter REVISION HISTORY Revision Date 1.0.0 02/14/2011 Initial release of datasheet 1.1.0 10/13/2011 Added Moisture Sensitivity Level (MSL) information 02/12/2013 Reformat of datasheet Changed min operating input voltage from 4.75V to 4.5V Updated Electrical Specifications parameter (quiescent current, feedback voltage, high and low side switch on-resistance, oscillator frequency, EN shutdown threshold voltage and hysteresis, EN lockout threshold voltage and hysteresis, UVLO threshold and hysteresis, soft-start time) Updated figure 2: XRP7665 block diagram Updated Pin Description, EN pin description Updated all Typical Performance Characteristics curves 3/29/2013 Updated Enable pin description Deleted Electrical Specification parameters (shutdown supply current, EN shutdown threshold voltage and hysteresis, EN lockout threshold voltage and hysteresis) Added Electrical Specification parameters (EN enable threshold voltage and hysteresis) Added “ENABLE FUNCTION” paragraph to the theory of operation section. 2.0.0 2.0.1 Description FOR FURTHER ASSISTANCE Email: customersupport@exar.com powertechsupport@exar.com Exar Technical Documentation: http://www.exar.com/TechDoc/default.aspx? EXAR CORPORATION HEADQUARTERS AND SALES OFFICES 48720 Kato Road Fremont, CA 94538 – USA Tel.: +1 (510) 668-7000 Fax: +1 (510) 668-7030 www.exar.com NOTICE EXAR Corporation reserves the right to make changes to the products contained in this publication in order to improve design, performance or reliability. EXAR Corporation assumes no responsibility for the use of any circuits described herein, conveys no license under any patent or other right, and makes no representation that the circuits are free of patent infringement. Charts and schedules contained here in are only for illustration purposes and may vary depending upon a user’s specific application. While the information in this publication has been carefully checked; no responsibility, however, is assumed for inaccuracies. EXAR Corporation does not recommend the use of any of its products in life support applications where the failure malfunction of the product can reasonably be expected to cause failure of the life support system or to significantly affect safety or effectiveness. Products are not authorized for use in such applications unless EXAR Corporation receives, writing, assurances to its satisfaction that: (a) the risk of injury or damage has been minimized; (b) the user assumes such risks; (c) potential liability of EXAR Corporation is adequately protected under the circumstances. or its in all Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited. © 2013 Exar Corporation 12/12 Rev. 2.0.1